How do you get rid of scars from shooting up?

You'll need some plastic surgery --- nothing too extensive. Recently, in urban areas (LA for certain, but others exist) there are doctor's outreach groups that specialize in the removal of gang signs (tatoos, brands, etc.). As they're using the plastic-surgical techniques you'll need to remove that scar tissue, and as they list in their mission statement the desire to help people improving their lives to leave stigma behind, these might be a perfect solution for you.